1. Field of the Invention
The present invention relates to branch-lane entry judging systems, and more particularly, to a branch-lane entry judging system that recognizes a branch lane by detecting traffic lines around a vehicle in which the branch-lane entry judging system is mounted and that judges whether the vehicle will enter the branch lane.
2. Description of the Related Art
In recent years, cruise control systems and adaptive cruise control (hereinafter abbreviated as ACC) systems have been developed. A cruise control system recognizes road conditions in front of and around a vehicle, and a preceding vehicle according to the result of analysis of an image taken by an image-taking device, such as a stereo camera or a monocular camera, or the result of measurement made by a radar device such as an infrared laser radar or a millimeter-wave radar. On the basis of the recognition result, the cruise control system performs constant-speed running control on the vehicle. An ACC system performs not only constant-speed running control on the vehicle, but also adaptive cruise control with a preceding-vehicle follow function of controlling the running of the vehicle following the preceding vehicle (for example, see Japanese Unexamined Patent Application Publication No. 2005-1566).
The ACC system normally causes the vehicle to run at a preset constant speed. When there is a preceding vehicle, the ACC system automatically and properly controls an accelerator throttle and a brake mechanism of the vehicle so that the vehicle follows the preceding vehicle.
When the vehicle enters a branch lane on the right or left side of a road such as an expressway, a freeway, or an ordinary road, it normally needs to be decelerated. However, while the ACC system stays in operation, the vehicle continues constant-speed running. For this reason, it is necessary for the driver to stop the cruise control function, for example, by performing hard braking or manually stopping the ACC system.
In order to cope with this problem, a branch-lane entry estimating apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2004-341941 estimates whether the vehicle is running near a branch point on the road according to map information from a navigation system, and detects stationary objects existing on the roadside, for example, delineators and guardrails. On the basis of the positional relationship with the objects, it is judged whether the vehicle is in a branch lane or whether the vehicle is likely to enter the branch lane.
Unfortunately, a stationary object, such as a delineator or a guardrail, is not always provided in every branch lane. Moreover, the positional relationship, such as the distance between a lane defined by traffic lines shown by continuous lines or broken lines on the road and the stationary object, is not always fixed. Therefore, it is not always easy to precisely specify the number and positions of lanes on the basis of the stationary object. Further, the above-described estimation is not properly performed if a rod-shaped stationary object standing up from the road surface, such as a delineator, is not detected accurately. For this reason, the above-described branch-lane entry estimating apparatus can be used only in a road environment that is ideal for the apparatus. If the apparatus is used in an unsuitable environment, an incorrect estimation may be made.
In the present invention, continuous lines and broken lines marked on the road surface, for example, a road center line such as a no-passing line, a vehicle-lane boundary line, and a separating line for separating a side strip and a roadway, are referred to as traffic lines. Further, a traffic line that is marked, for example, at a branch point on the expressway, as shown in FIG. 5 that will be described below, and that is wider and shorter than a normal traffic line is referred to as a block line.
For example, when the vehicle enters a branch lane at the entrance of a parking area or at an interchange during running on the expressway, it is necessary to relatively quickly change the running state of the vehicle, for example, by hard braking. Therefore, control different from control for running in a normal lane is required. Similar control is necessary not only in the expressway, but also in a branch lane from a bypass of a national road to an ordinary road and a branch lane from an ordinary road to a side road.
For that purpose, such an apparatus is first required to accurately detect the existence of a branch lane, and to accurately judge whether the vehicle will enter the detected branch lane.